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Results for “Acoustical effects”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Vibrations of three-dimensional pipe systems with acoustic coupling

A general algorithm is developed to calculate the beam-type dynamic response of three dimensional multiplane finite length pipe systems, consisting of elbow and straight ducts with continuous interfaces. Emphasis is on secondary acoustic wave effects giving rise to coupling mechanisms; and the simulation accounts for one-dimensional elastoacoustic coupling from a plane acoustic wave and secondary loads resulting from wave asymmetries. The transfer matrix approach is adopted in modeling the elastodynamics of each duct, with allowance for distribution loads. Secondary loads from plane wave distortion are considered with a solution of the Helmholtz equation in an equivalent rigid waveguide, and effects of path imperfection are introduced as a perturbation from the hypothetical perfectly straight pipe. Computations indicate that the one-dimensional acoustic assumption is valid for frequencies below one-half the first cut-off frequency, and the three-dimensional acoustic effects produce an increase in response levels near and above cut-off.

El-Raheb, M.↗
NASA NTRS1977

Increase in effectiveness of low frequency acoustic liners by use of coupled Helmholtz resonators

Coupling of Helmholtz resonators in a low-frequency absorber array was studied as a means for increasing the effectiveness for absorbing low-frequency core engine noise. The equations for the impedance of the coupled-resonator systems were developed in terms of uncoupled-resonator parameters, and the predicted impedance for a parallel-coupled scheme is shown to compare favorably with measurements from a test model. In addition, attenuation measurements made in a flow duct on test coupled-resonator panels are shown to compare favorably with predicted values. Finally, the parallel-coupled concept is shown to give significantly more attenuation than that of a typical uncoupled resonator array of the same total volume.

Dean, L. W.↗
DOE OSTI2023

High-Resolution Near-Surface Imaging at the Basin Scale Using Dark Fiber and Distributed Acoustic Sensing: Toward Site Effect Estimation in Urban Environments

Near-surface seismic structure, particularly the shear wave velocity (V s ), can strongly affect local site response, and should be accurately estimated for ground motion prediction during seismic hazard assessment. The Imperial Valley (California), occupying the southern end of the Salton Trough, is a seismically active basin with thick surficial lacustrine sedimentary deposits. In this study, we utilize ambient noise records and local earthquake events for high-resolution near-surface characterization and site effect estimation with an unlit fiber-optic telecommunication infrastructure (dark fiber) in Imperial Valley by using the distributed acoustic sensing (DAS) technique. We apply ambient noise interferometry to retrieve coherent surface waves from DAS records, and evaluate performances of three different surface wave methods on DAS ambient noise dispersion imaging. We develop a quality control workflow to improve the dispersion measurement of noisy portions of the DAS data set by using a data selection strategy. Using the joint inversion of both the fundamental mode and higher overtones of Rayleigh waves, a high resolution two-dimensional (2D) V s structure down to 70 m depth is obtained. We successfully achieve an improved V s 30 (the time-averaged shear-wave velocity in the top 30 m) model with higher spatial-resolution and reliability compared to the existing community model for the area. We also explore the potential for utilizing DAS earthquake events for site amplification estimation. The preliminary results reveal a clear anti-correlation between the approximated site response and the V s 30 profile. In conclusion, our results indicate the potential utility of DAS deployed on dark fiber for near-surface characterization in appropriate contexts.

58 GEOSCIENCES↗
NASA NTRS2018

Measurement of Noise Reduction from Acoustic Casing Treatments Installed over a Subscale High Bypass Ratio Turbofan Rotor

NASA is continuing to develop over-the-rotor acoustic liners for turbofan applications. A series of low Technology Readiness Level experiments were conducted to better understand the acoustic and aerodynamic effects of these acoustic liners. The final experiment included the evaluation of four acoustic casing treatment concepts and two baseline configurations in an internal flow axial compressor facility with a 1.5 pressure-ratio high-bypass turbofan rotor. An inlet in-duct array was utilized to extract sound power levels propagating forward from the turbofan rotor. The effect of a circumferentially grooved relative to a hardwall fan case was found to reduce the in-duct sound power level by about 1.5dB for frequencies less than 2kHz while increasing noise from 4 to 8kHz by as much as 7.5dB at low fan speeds. The four acoustic treatment concepts were incorporated into the bottoms of the circumferential grooves and found to provide an additional 1 to 2dB sound power level reduction under 2kHz. The sound power level reduction was found to be even greater, 2.5 to 3.5dB, when evaluating the reduction on rotor alone duct modes (co-rotating modes). The acoustic treatments also appeared to reduce multiple pure tone noise at transonic fan speeds. Depending on the acoustic treatment concept, the high-frequency noise created by the circumferential grooves was reduced by 1.5 to 5 dB. The total noise reduction from acoustic treatments embedded into the bottoms of circumferential grooves relative to a hardwall baseline was found to be 2.5 to 3.5dB sound power level. The sound power level reduction for rotor alone (co-rotating) modes was found to be 3.5 to 4.5dB. These results show the potential for significant turbofan noise reduction by incorporating acoustic treatments over-the-rotor.

Noise↗
NASA NTRS2018

Measurement of Noise Reduction from Acoustic Casing Treatments Installed Over a Subscale High Bypass Ratio Turbofan Rotor

NASA is continuing to develop over-the-rotor acoustic liners for turbofan applications. A series of low Technology Readiness Level experiments were conducted to better understand the acoustic and aerodynamic effects of these acoustic liners. The final experiment included the evaluation of four acoustic casing treatment concepts and two baseline configurations in an internal flow axial compressor facility with a 1.5 pressure-ratio high-bypass turbofan rotor. An inlet in-duct array was utilized to extract sound power levels propagating forward from the turbofan rotor. The effect of a circumferentially grooved relative to a hardwall fan case was found to reduce the in-duct sound power level by about 1.5dB for frequencies less than 2kHz while increasing noise from 4 to 8kHz by as much as 7.5dB at low fan speeds. The four acoustic treatment concepts were incorporated into the bottoms of the circumferential grooves and found to provide an additional 1 to 2dB sound power level reduction under 2kHz. The sound power level reduction was found to be even greater, 2.5 to 3.5dB, when evaluating the reduction on rotor alone duct modes (co-rotating modes). The acoustic treatments also appeared to reduce multiple pure tone noise at transonic fan speeds. Depending on the acoustic treatment concept, the high-frequency noise created by the circumferential grooves was reduced by 1.5 to 5 dB. The total noise reduction from acoustic treatments embedded into the bottoms of circumferential grooves relative to a hardwall baseline was found to be 2.5 to 3.5dB sound power level. The sound power level reduction for rotor alone (co-rotating) modes was found to be 3.5 to 4.5dB. These results show the potential for significant turbofan noise reduction by incorporating acoustic treatments over-the-rotor.

Aeroacoustics↗
NASA NTRS1993

The influence of source acceleration on acoustic signals

The effect of aircraft acceleration on acoustic signals is often ignored in both analytical studies and data reduction of flight test measurements. In this study, the influence of source acceleration on acoustic signals is analyzed using computer simulated signals for an accelerating point source. Both rotating and translating sources are considered. Using a known signal allows an assessment of the influence of source acceleration on the received signal. Aircraft acceleration must also be considered in the measurement and reduction of flyover noise. Tracking of the aircraft over an array of microphones enables ensemble averaging of the acoustic signal, thus increasing the confidence in the measured data. This is only valid when both the altitude and velocity remain constant. For an accelerating aircraft, each microphone is exposed to differing flight velocities, Doppler shifts, and smear angles. Thus, averaging across the array in the normal manner is constrained by aircraft acceleration and microphone spacing. In this study computer simulated spectra, containing acceleration, are averaged across a 12 microphone array mimicking a flight test with accelerated profile in which noise data was obtained. Overlapped processing is performed is performed in the flight test measurements in order to alleviate spectral smearing.

Kelly, Jeffrey J.↗
NASA NTRS2003

Nonlinear Resonant Oscillations of Gas in Optimized Acoustical Resonators and the Effect of Central Blockage

Optimizing resonator shapes for maximizing the ratio of maximum to minimum gas pressure at an end of the resonator is investigated numerically. It is well known that the resonant frequencies and the nonlinear standing waveform in an acoustical resonator strongly depend on the resonator geometry. A quasi-Newton type scheme was used to find optimized axisymmetric resonator shapes achieving the maximum pressure compression ratio with an acceleration of constant amplitude. The acoustical field was solved using a one-dimensional model, and the resonance frequency shift and hysteresis effects were obtained through an automation scheme based on continuation method. Results are presented for optimizing three types of geometry: a cone, a horn-cone and a half cosine-shape. For each type, different optimized shapes were found when starting with different initial guesses. Further, the one-dimensional model was modified to study the effect of an axisymmetric central blockage on the nonlinear standing wave.

Li, Xiaofan↗
NASA NTRS2003

Nonlinear Resonant Oscillations of Gas in Optimized Acoustical Resonators and the Effect of Central Blockage

Optimizing resonator shapes for maximizing the ratio of maximum to minimum gas pressure at an end of the resonator is investigated numerically. It is well known that the resonant frequencies and the nonlinear standing waveform in an acoustical resonator strongly depend on the resonator geometry. A quasi-Newton type scheme was used to find optimized axisymmetric resonator shapes achieving the maximum pressure compression ratio with an acceleration of constant amplitude. The acoustical field was solved using a one-dimensional model, and the resonance frequency shift and hysteresis effects were obtained through an automation scheme based on continuation method. Results are presented for optimizing three types of geometry: a cone, a horn-cone and a half cosine- shape. For each type, different optimized shapes were found when starting with different initial guesses. Further, the one-dimensional model was modified to study the effect of an axisymmetric central blockage on the nonlinear standing wave.

Li, Xiao-Fan↗
NASA NTRS2014

An Evaluation of the Additional Acoustic Power Needed to Overcome the Effects of a Test-Articles Absorption During Reverberant Chamber Acoustic Testing of Spaceflight Hardware

It is important to realize that some test-articles may have significant sound absorption that may challenge the acoustic power capabilities of a test facility. Therefore, to mitigate this risk of not being able to meet the customers target spectrum, it is prudent to demonstrate early-on an increased acoustic power capability which compensates for this test-article absorption. This paper describes a concise method to reduce this risk when testing aerospace test-articles which have significant absorption. This method was successfully applied during the SpaceX Falcon 9 Payload Fairing acoustic test program at the NASA Glenn Research Center Plum Brook Stations RATF.

sound power↗
DOE OSTI2021

Line confusion in spectroscopic surveys and its possible effects: shifts in Baryon Acoustic Oscillations position

ABSTRACT Roman Space Telescope will survey about 17 million emission-line galaxies over a range of redshifts. Its main targets are Hα emission-line galaxies at low redshifts (z < 2) and [O iii] emission-line galaxies at high redshifts (z > 2). The Roman Space Telescope will estimate the redshift of these galaxies with single-line identification. This suggests that other emission-line galaxies may be misidentified as the main targets. In particular, it is hard to distinguish between the H β and [O iii] lines as the two lines are close in wavelength and hence the photometric information may not be sufficient to separate them reliably. Misidentifying H β emitter as [O iii] emitter will cause a shift in the inferred radial position of the galaxy by approximately 90 Mpc h−1. This length-scale is similar to the Baryon Acoustic Oscillation (BAO) scale and could shift and broaden the BAO peak, possibly introduce errors in determining the BAO peak position. We qualitatively describe the effect of this new systematic and further quantify it with a light-cone simulation with emission-line galaxies. Our results show a systematic shift in the recovered isotropic BAO positions that depends on the percentage of interlopers (percentage of ${\rm H}\,\beta$) in the sample. The systematic shift can be as large as $0.1{-}0.3\,\mathrm{ per}\,\mathrm{ cent} \, {\rm x}\, {{\%}}{\rm H}\,\beta$ for analysis performed at redshifts z = 1.3−1.9.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1976

Investigation of the effects of a moving acoustic medium on jet noise measurements

Noise from an unheated sonic jet in the presence of an external flow is measured in a free-jet wind tunnel using microphones located both inside and outside the flow. Comparison of the data is made with results of similar studies. The results are also compared with theoretical predictions of the source strength for jet noise in the presence of flow and of the effects of sound propagation through a shear layer.

Cole, J. E., III↗
NASA NTRS2014

An Evaluation of the Additional Acoustic Power Needed to Overcome the Effects of a Test-Article's Absorption during Reverberant Chamber Acoustic Testing of Spaceflight Hardware

The exposure of a customers aerospace test-article to a simulated acoustic launch environment is typically performed in a reverberant acoustic test chamber. The acoustic pre-test runs that will ensure that the sound pressure levels of this environment can indeed be met by a test facility are normally performed without a test-article dynamic simulator of representative acoustic absorption and size. If an acoustic test facilitys available acoustic power capability becomes maximized with the test-article installed during the actual test then the customers environment requirement may become compromised. In order to understand the risk of not achieving the customers in-tolerance spectrum requirement with the test-article installed, an acoustic power margin evaluation as a function of frequency may be performed by the test facility. The method for this evaluation of acoustic power will be discussed in this paper. This method was recently applied at the NASA Glenn Research Center Plum Brook Stations Reverberant Acoustic Test Facility for the SpaceX Falcon 9 Payload Fairing acoustic test program.

acoustic↗
NASA NTRS2014

An Evaluation of the Additional Acoustic Power Needed to Overcome the Effects of a Test-Article's Absorption During Reverberant Chamber Acoustic Testing of Spaceflight Hardware

The exposure of a customer's aerospace test-article to a simulated acoustic launch environment is typically performed in a reverberant acoustic test chamber. The acoustic pre-test runs that will ensure that the sound pressure levels of this environment can indeed be met by a test facility are normally performed without a test-article dynamic simulator of representative acoustic absorption and size. If an acoustic test facility's available acoustic power capability becomes maximized with the test-article installed during the actual test then the customer's environment requirement may become compromised. In order to understand the risk of not achieving the customer's in-tolerance spectrum requirement with the test-article installed, an acoustic power margin evaluation as a function of frequency may be performed by the test facility. The method for this evaluation of acoustic power will be discussed in this paper. This method was recently applied at the NASA Glenn Research Center Plum Brook Station's Reverberant Acoustic Test Facility for the SpaceX Falcon 9 Payload Fairing acoustic test program.

absorption↗
NASA NTRS1979

Acoustic scattering by circular cylinders of various aspect ratios

The effects of acoustic scattering on the useful frequency range of pressure gradient microphones were investigated experimentally between ka values of 0.407 and 4.232 using two circular cylindrical models (L/D = 0.5 and 0.25) having a 25 cm outside diameter. Small condenser microphones, attached to preamplifiers by flexible connectors, were installed from inside the cylindrical bodies, and flush mounted on the exterior surface of the cylinders. A 38 cm diameter woofer in a large speaker enclosure was used as the sound source. Surface pressure augmentation and phase differences were computed from measured data for various sound wave incidence angles. Results are graphically compared with theoretical predictions supplied by NASA for ka = 0.407, 2.288, and 4.232. All other results are tabulated in the appendices. With minor exceptions, the experimentally determined pressure augmentations agreed within 0.75 dB with theoretical predictions. The agreement for relative phase angles was within 5 percent without any exceptions. Scattering parameter variations with ka and L/D ratio, as computed from experimental data, are also presented.

Maciulaitis, A.↗
NASA NTRS2002

Nonlinear Internal Waves in the South China Sea During ASIAEX

Internal wave distribution maps have been compiled from more than one hundred ERS-1/2, RADARSAT and Space Shuttle SAR images in the South China Sea (SCS) from 1993 to 2000. Based on these distribution maps, most of internal waves in the northeast part of SCS were propagating westward. The wave crest can be as long as 200 km with amplitude of 100 m, due to strong current from the Kuroshio branching out into the SCS. In recent Asian Seas International Acoustics Experiment (ASIAEX), moorings have been deployed in April 2000 and May 2001. Simultaneous RADARSAT ScanSAR images have been collected during the field test to integrate with the model and the in-situ measurements in the SCS. During ASIAEX in May 2001, many large internal waves were observed at the test area and were the major features for acoustic volume interaction. The environmental parameters have been calculated based on extensive CTD castings and mooring data. Nonlinear internal wave models have been applied to simulate the wave evolution on the continental shelf and the results compare reasonably with mooring measurements. The evolution and dissipation of huge internal waves on the shelf break, mode-two waves, elevation waves, and wave-wave interaction are very important issues for acoustic propagation. The implication of internal wave effects on acoustic propagation will also be discussed.

ACOUSTIC PROPAGATION↗
NASA NTRS2003

Pulsed-Source Interferometry in Acoustic Imaging

A combination of pulsed-source interferometry and acoustic diffraction has been proposed for use in imaging subsurface microscopic defects and other features in such diverse objects as integrated-circuit chips, specimens of materials, and mechanical parts. A specimen to be inspected by this technique would be mounted with its bottom side in contact with an acoustic transducer driven by a continuous-wave acoustic signal at a suitable frequency, which could be as low as a megahertz or as high as a few hundred gigahertz. The top side of the specimen would be coupled to an object that would have a flat (when not vibrating) top surface and that would serve as the acoustical analog of an optical medium (in effect, an acoustical "optic").

Shcheglov, Kirill↗
NASA NTRSDate not supplied

NASA Investigation of Flow Direction Effects on Impedance Eduction for Acoustic Liners

In support of a collaboration with the International Forum for Aviation Research (IFAR), the NASA Langley Liner Physics Team has acquired a detailed dataset for use in the evaluation of flow direction effects on the acoustic liner impedance eduction process. Measurements are acquired with four acoustic liners designed to cover a range of sensitivities to source sound pressure level and tangential mean flow effects, specifically at source levels of 120 and 140 dB and centerline Mach numbers of 0.0, 0.1, 0.2, and 0.3. These measurements include detailed flow profile surveys upstream and downstream of the liner test window, as well as acoustic pressure data over the extent of the test window. The results clearly demonstrate the importance of the choice of Mach number used in the impedance eduction analysis. Average Mach number differences of less than 0.01 result in significant variation in the educed impedance spectra. These data will soon be supplied to the IFAR partners and will be made available for the general public within the next year.

acoustic↗